1. Field of the Invention
This invention relates in general to gas detecting devices and in particular to a new and useful method and apparatus for determining one component of very low concentration of a test gas.
The invention particularly concerns a process for determing one component of very low concentration in a test gas, which is guided in a supply line to concentrate the component across a sample collector, whose amassed quantity of the sample is relinquished to a detection sensor. Furthermore, the invention deals with an arrangement to carry out the process.
In U.S. Pat. No. 4,277,251, on the example of measuring the alcohol content of expired air, a process is employed whereby the breath sample is conveyed through a sample collector, absorbing the alcohol component, and is collected. After the sample is taken, the sample collector is heated, which drives out the absorbed gas and carries it to an attached meter.
However, it is a disadvantage, that during the entire sample collection process of the familiar method, it is not possible to monitor or even measure the gas being investigated for its components. Accordingly, the measurement process is divided into two interdependent successive steps, namely, first the sample collection, during which no measurement can be done, and then the investigation of the sample, during which no new collection can be undertaken. A measuring instrument working with such familiar measurement procedures, therefore, is not capable of measurement during the sample collection. Furthermore, the familiar method is only reliable and informative when the investigated gas contains only one component that is to be detected. For in this case, the material taking up the component in the sample collector and the sensitivity of the measurement instrument can be calibrated against each other. If, however, several components are contained in the test gas, which can be concentrated in the sample collector, then during the subsequent driving off they are all carried to the detection sensor. A separate, component-specific detection of the individual concentrations of individual components are suspected in the test gas. With a collective analysis in the detection sensor, these could produce spurious measurement results by virtue of the socalled cross sensitivity, or the sensitivity of the meter not specific to the type of gas.